Method for agglomerating finely divided materials

ABSTRACT

AN IMPROVED METHOD FOR AGGLOMERATING FINELY DIVIDED POWDERS IS DISCLOSED. THE METHOD INVOLVES INTRODUCING A FINELY DIVIDED MATERIAL, SUCH AS CLAY, WHICH HAS A MINIMUM LEVEL OF A WETTING AGENT, INTO A ROTATING DRUM; TUMBLING THE MATERIAL IN THE DRUM AND THEREAFTER CONTACTING THE TUMBLING MATERIAL WITH A LIQUID WETTING AGENT AT A POINT WHEREIN THE MATERIAL BEGINS TO CURL AND TUMBLE BACK OVER ITSELF. CERTAIN CRITICAL SPRAY ANGLES AND ANGLES OF INCLINATION ARE DISCLOSED. THE AGGLOMERATED PRODUCT IS FREE-FLOWING WITH NEGLIGIBLE DUSTING AND HAS A SIZE RANGE WHICH EXHIBITS MAXIMUM EFFECTIVE PACKING DENSITY AND ATTRITION RESISTANCE.

6 Sheets-Sheet 1 April 1974 R. B. TAKEWELL. ETAL METHOD FORAGGLOMERATING FINELY DIVIDED MATERIALS Filed OCt. 4, 1971 6 Sheets-Sheet2 r zal R. B. TAKEWELL ETAL METHOD FOR AGGLOMERATING FINELY DIVIDEDMATERIALS April 9, 1974 Filed Oct. 4, 1971 FIG. 9

April 9, 1974 I R. B. TAKEWELL ETAL 3,803,283

METHOD FOR AGGLOMERATING FINELY DIVIDED MATERIALS Filed Oct. 4, 1971 6Sheets-Sheet 3 VIEW CC FIG. 3

April 9, 1974 R. B. TAKEWELL ETAL 3,803,233

METHOD FOR AGGLOMERATING FINELY DIVIDED MATERIALS Filed Oct. 4, 1971 6SheetsSheet 4 FIG. 4

FIG. 5

April 9, 1974 R. B-TA WELL ErAL 3,803,283

METHOD FOR AGGLOMERATING FINELY DIVIDED MATERIALS Filed Oct. 4, 1971 sSheets-Sheet 5 FIG.7

FIG. 60

FIG. IO

F|G.6b

A ril 9, 1974 R. B. TAKEWELL ETAL 3,303,233

METHOD FOR AGGLOMERATING FINELY DIVIDED MATERIALS Filed Oct. 4, 1971 6Sheets-Sheet 6 VIEW B-B FIG. l2

United States l atent O 3,803,283 METHOD FOR AGGLOMERATING FINELYDIVIDED MATERIALS Robert B. Takewell, Borger, Tex., Paul W. Brandon,

Havre de Grace, Md., and Paul R. Odom, Macon, Ga.,

assignors to J. M. Huber Corporation, Locust, NJ.

Filed Oct. 4, 1971, Ser. No. 186,113 Int. Cl. B01j 2/12 US. Cl. 264-1172 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Ingeneral, the present invention involves agglomeration of finely dividedmaterial and more specifically relates to methods for wet pelletizingfinely divided mineral and like substances into pellets of anadvantageous pellet size distribution which achieves optimum bulkdensity with free flowing characteristics for shipping, packaging, andstoring and reduces the amount of fines present while maintaining highdispersibility of the product.

Many powdery materials such as degritted and delaminated dry clay aredusty, non free-flowing and have a low bulk density of around 25 poundsper cubic foot. In order to induce such materials to flow from tanks,hoppers and chutes and other containers, vibrators, air pads, or hammershave to be used in order to prevent the fluffy material from caking orbridging. A finely divided material such as refined clay is very dustyin the dry state and, even with the best of air-tight containers andshipping vessels, much loss of the product and contamination of thesurrounding environment occurs.

Apparatus revealed by the prior art for agglomerating finely dividedpowders include pin mixer type pelletizers and rotating tilted panpelletizers. Materials pelletized in these devices achieve a fairly goodcompaction but produce pellets which are friable and substantiallyuniform in size. Also these devices produce fines and dust along withthe pellets so that the dust problem is only reduced and not eliminated.The pellets are denser than the powdery material but not of the optimumdensity for shipping and dispersion.

The prior art has suffered from the difiiculty of obtaining a pelletsize distribution which allows the pellets to be placed in containersand storage vessels in the most compact manner. For example, pourdensities of kaolin clays pelletized by methods of the prior art such asthose disclosed by US. Pats. 3,446,218, 3,542,534, 3,460,195 and2,758,039, usually range from 50 to 55 pounds per cubic foot, whereasthe kaolin clays pelleted by the present invention exhibit pourdensities in the range of 60 to 70 pounds per cubic foot.

Other deficiencies of the prior art processes include the high rate ofattrition among the individual pellets in their containers which resultsin a large amount of undesirable fines. In order to reduce the attritionrate and prevent material loss and plant contamination due to excessivefines content, some of the prior art devices are 'ice designed toproduce a hard pellet. While in some instances this serves to reduce theloss to fines, it always results in a pellet which is difiicult tofracture and disperse into the final product such as paint, paper, ink,rubber, etc.

Also, the prior art processes include methods which call for adding allof the moisture for pelletizing to the substance before it is introducedinto the pelletizer. This procedure even further reduces the flowabilityof the material and necessitates special conveying equipment such asscrew conveyors to move the material from the wetting chamber to thepelletizer. Since the wetted material, having from 5 to 20% or highermoisture level, is especially susceptible to caking in the moist state,it is difficult to convey smoothly.

Other existing devices add all of the water of pelletization to thematerial while it is in the pelletizer. This results in a dry powderyproduct being introduced into the pelletizer which causes a large amountof dust in and around the pelletizer arising from the powdery materialbecoming airborne. Also the completely dry material in the pelletizer ismore difiicult to wet evenly than would be a slightly damp material justas dry sponge is less absorbent than a slightly damp one.

SUMMARY OF THE INVENTION Accordingly it is an object of this inventionto provide new and highly effective methods for pelletizing powdered orfinely divided material and overcoming the deficiencies of the prior artabove.

It is further an object of this invention to provide an agglomeratingprocess which produces an optimum pellet size distribution for maximumbulk density with free flowing characteristics of the agglomeratedmaterial.

It is also an object of this invention to reduce the amount of materialloss through attrition and fines in the pelletizer and in the shippingcontainer.

It is still a further object of this invention to provide an improvedmethod for agglomerating loose material into pellets which are easilydispersed in the final products in which they are used.

It is another object to densify powdered material into agglomerateswhich are free-flowing and nondusting.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings.

The present invention overcomes the deficiences of the prior art andachieves its objectives by providing an improved method that produces anagglomerated product which most efiiciently utilizes shipping space byfilling up the voids which naturally occur between spherically shapedequal-sized particles packed in bulk containers such as bags, boxes,tanks, or railroad cars, and which exhibits free-flowing characteristicswith negligible dusting.

BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate theunderstanding of this invention, reference will now be made to appendeddrawings of preferred embodiments of the present invention. The drawingsshould not be construed as limiting the invention but are exemplaryonly.

In the drawings:

FIG. 1 is a diagram of the pelletizing process of the present invention.

FIG. 2 is a partially cutaway side view of a rotating drum pelletizer ofthe present invention.

FIG. 3 is a cross-sectional view of the rotating drum pelletizer of thepresent invention taken at section line CC of the drum.

FIG. 4 is an external view of the inlet end of the pel letizer drum ofthe present invention.

FIG. 5 is an external view of the outlet end of the pelletizer drum.

FIG. 6a is a front view of the spray nozzle used to inject the binderfluid into the pelletizer.

FIG. 6b is a side view of the spray nozzle.

5 FIG. 7 1s a cross-sectional view of conventional pellets.

FIG. 8 is a cross-sectional view of pellets produced by the process ofthe present invention.

FIG. 9 is a top view of the rotating drum of this invention.

FIG. 10 is a schematic diagram of a further embodiment of the presentinvention.

FIG. 11 is a cross-sectional view of the drum at A-A.

FIG. 12 is a cross-section of the drum at B-B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS be pelletized is obtained byincomplete drying of the material during wet processing or by addingmoisture to the dry product prior to pelletizing. For instance in theclay industry, a raw kaolin clay, after being mined, is suspended in anaqueous slurry and degritted, classified and/or delaminated and thendried. In applying the agglomerating process of this invention, the clayslurry is only partially dried to the extent that it contains from 1V2%to about 5% moisture, and then it is agglomerated according to theteachings of the present invention.

If the powdered material contains less than 1 /2% moisture then asufiicient amount of wetting liquid can be applied to it prior toentering the drum as for example, in pin auger 2, to bring its moisturelevel up to l /2% to about 5%. The finely divided material to beagglomerated, having the minimum amount of moisture in it, is added tothe pelletizing drum 1 and wetted by spray 8 as it is tumbled. Thepreadded moisture induces the finely divided material to more readilyaccept the bulk of the wetting liquid added in the drum 1. Thepre-wetting also results in a reduction of dust in the drum andconveying systems. It also provides an easily flowing blend which isless susceptible to caking.

The material in the drum receives the remainder of wetting liquidthrough pelletizer liquid supply line 56 which feeds the liquid to spraynozzle 8 located within the drum 1. The liquid is sprayed from spray 8onto the material and the material is pelletized by the rotating motionif the drum 1 and is passed through the drum outlet 14 to the pelletconveyor 6. The drum 1 has removable manholes 66, shown in FIG. 2,opening into the drum to allow access to the inside of the drum formaintenance. The manholes 66 can also be used to purge material from thedrum when changing operation from one type of material to another orchanging grades of material.

Referring to FIGS. 2 and 4, the rotating drum 1 receives materialthrough drum inlet 15 which is a substantially cylindrical sectionpermanently attached to one end of the drum and is supported by floorsupports 16 and rotatably attached to the floor supports 16 by trunionbearings 13. A conveyor 2 such as a screw conveyor passes concentricallythrough the drum inlet 15 to bring material into the drum. A closure isobtained by lubricated bushings 17 between the conveyor 2 and the inlet15.

In the drum 1 perpendicular to the longitudinal axis are bafiles 3 and7, FIG. 1, containing openings to allow the material to progress throughthe drum. The baflies divide the drum into three chambers to providethree different functions. Bafile 3 is located near the middle of thedrum length and forms the pelletizing chamber 39 at the inlet end of thedrum. Bafile 7 divides the remaining portion of the drum into twochambers, a polishing chamber 40, and a discharge chamber 41 containingone or more lifter trays 42.

At the downstream end of the drum 1, the drum outlet 14 may contain atapered or right cylindrical discharge cone 43 concentrically locatedwithin outlet 14 to allow finished pellets to flow into discharge spout9. From the discharge spout 9, the pellets drop into pellet conveyor 6to 'be removed from the pelleting drum area.

A wetting liquid is supplied to spray 8 through line 56 and may consistof water and/or steam or air. Water is supplied through line 5a and arotameter 47. Steam or air enters through steam-air line 44 andsteam-air valve 45.

In FIG. 3, the pelletizer drum 1 contains a bed of material 18 beingpelletized by continuously tumbling down the side of the shell. At thepoint 19 on the inner surface of the bed 18 where the material begins tobreak loose from the bed and tumble down towards the bottom of theshell, due to the increasing angle of repose, force of gravity, andforces arising from the drum rotation, the wetting liquid is mostadvantageously sprayed. This point 19 is referred to as the curl in thetumbling bed of material 18.

The spray attitude angle 48 is the angle the spray makes with a verticalline through the axis of rotation of the drum 1. This angle ispreferably around 45-50 but can range from 35 to depending upon thespeed of rotation of the drum and the material being agglomerated. At adrum speed of 6 rpm, the preferable angle is around 45.

The spray of liquid is directed at the material near the upstream end 49of the drum 1 but is not allowed to contact the end 49.

In FIGS. 2 and 4, the drum 1 has a concentrical inlet section 15 whichis permanently attached thereto and rotates with the drum. A nonrotatingconveyor system 2 passes concentrically through the inlet section 15 andis attached thereto by lubricated bushings 17. The conveyor system 2 issupported by support 20 passing beneath it.

FIGS. 2 and 5 disclose the pellet outlet 14 concentrically located inthe end 21 of the drum. =Floor support 16 supports brackets 22 whichsupport the trunion bearing 13 mounted adjacent the drum outlet 14.

In FIGS. 6a and 6b, the spray nozzle 8 emits a flat, wide spray ofbinder fluid which forms a pattern with spray angle 23 and sprayinclination 24. Angle 23 is about 30 and spray inclination 24 is alsoaround 30.

In FIGS. 7 and 8, the advantageous pellet size distribution isexhibited, with FIG. 7 showing the prior art uniform size pellets 26packed in bulk and FIG. 8 showing the pellets 27 of this invention alsopacked in bulk. The pellets 26 of FIG. 7 have many void spaces 25between them resulting in a waste of space and also allowing relativelylarge movements and attrition between the pellets during transportationand handling. FIG. 8 shows how the pellet size distribution of thepresent invention results in the voids 25 between large pellets 27,being filled with intermediate pellets 28, small pellets 29, and verysmall pellets 30. Thus FIG. 8 shows how packaging and shipping space isutilized very efiiciently and how the close packing of pellets reducesrelative movement between them and reduces attrition and fines.

In FIG. 9, the rotating drum 1 has permanently attached to the drum end21 a driven ring gear 10 which is constantly meshed with driving ringgear 11 on the shaft of driving motor 12. This arrangement providesrotation for the drum. Trunion bearings 13 rotatably support therotating drum. Pelleted material passes from the drum out outlet section14 and into pellet conveyor 6.

Raw powdered material enters the conveyor 2 at material inlet 34, isconveyed down the conveyor 2 which passes concentrically through theinlet section 15 and into the drum 1. The inlet section 15 ispermanently attached to the drum and is also rotatably supported bytrunion bearing 13. The conveyor is supported by and attached toconveyor support 20. The shaft 35 of the conveyor is connected to apulley 33 which is driven by motor 31.

In typical operation, the material to be agglomerated is stored instorage tank 35 and there allowed to deaerate by settling.

It has been found that deaerating the feed material prior toagglomerating it results in a more compact and desirable pellet and alsoreduces the amount of fines, since the pellets form faster in the drumwith the deaerated material than when it is not deaerated.

From the storage tank 35, the material is conveyed through line 4 toconveyor 2. It is metered by passing it through feeder valve 46. Asupply line 56 receives wetting liquid through valve 47 from tank 36 andfeeds this to spray nozzle 8 in the rotating drum 1.

Since the material to be pelletized should contain from 1 to 5% moisturefor best results, a prewetting supply line 50 is attached to the feedervalve 46 in order to supply moisture to the material if it contains lessthan l /2% moisture. If the material is already sufliciently damp, valve51 in line 50 can be closed to prevent excess prewetting.

The rotating drum is rotated at 6 r.p.m. and material is fed throughconveyor 2 and into the drum at approximately 10 tons/hour. A wettingliquid such as water or steam or both is sprayed into the curl 19 of thebed of material 18 as it breaks loose from the drum wall and tumbles tothe bottom of the drum.

When steam is used with water or by itself, it gives improved wettingability and results in better pellets which exit the pelletizer at ahigher temperature. The use of steam gives a greater spray pressure,finer droplets and mist, and less liquid surface tension. Air or othergases may also be used to aid in atomization. This results in a greaterpenetration into the bed of material and better dispersion of the liquidthroughout the material. Smaller droplets and better dispersion meansthat a given volume of liquid will go further and provide more evenwetting and a tighter control over the moisture content of the material.

The use of steam also provides a convenient method of adding heat to thepellets so that if they are to be dried later, less heat will berequired to dry them and they will dry more uniformly. Since heat andmoisture travel slowly through the dense agglomerated pellet, drying acool moist pellet results in drying the outer part of the pellet into ahard shell without removing all of the moisture near the center of thepellet. This process makes the pellet particularly susceptible tobreaking. When the pellet is formed at a temperature near thetemperature of vaporization of the wetting liquid, and is then dried,very little heat is required in the center of the pellet to vaporize thewetting liquid and remove it from the pellet. Thus the pellet driesuniformly from the inside out and is not case hardened as is thesituation when cool wet pellets are heated and dried. When steam is usedfor pelletizing, a desirable finished pellet temperature is from 65 to100 C.

Other suitable wetting liquids include one or more of the following:latex, oil, Petro A. G., silanes, stearates, starch, sizing agents,organic materials such as benzene, kerosene, alcohol, etc., organic orinorganic dispersing agents, dispersed and nondispersed clay and thelike.

If a very hard pellet is desired, a binder additive such as molasses ororganic liquid can be added to the dry powdered material, or to thewetting liquid supply line. In the alternative, the binder may besprayed separately in the drum from the wetting liquid.

The drum can be of any dimension depending upon the volume of materialto be agglomerated. In one preferred embodiment of this invention thedrum has a length of 12 feet and an inner diameter of 10 feet. Athroughput of about 250 pounds of material per minute and 25-35 poundsof liquid per minute (approximately 3 gallons per minute) gives oneffective bed depth of about 8 to 18 inches.

A preferable bed depth when pelletizing clay using steam and water isaround 10 inches. At this depth, a particularly desirable pellet sizedistribution is obtained. A deeper bed depth results in more largepellets and less small pellets.

It is believed that the pellets form in layers or laminations, beginningwith a seed or nucleus and gaining a layer each time the pellet istumbled in the presence of loose wet material or passes through thespray. Thus a deeper bed results in each pellet remaining in contactlonger with available loose material. Also a deeper bed results ingreater pressure on the pellets as they pass near the bottom of the bedand the results is a harder more compact pellet which may be difficultto disperse.

The production rate of the agglomerating apparatus of the presentinvention depends upon the size of the drum, the critical speed ofrotation of the drum for the type of material used, and the moistureinput rate.

The critical speed of the drum appears to be the speed at which thecentrifugal force acting upon the material reaches such a magnitude thatit interferes with the normal cascading action of the material in thedrum. Instead of cascading down upon itself, the bed of material is heldagainst the drum wall longer until it breaks loose and arcs across tothe opposite side of the drum causing discontinuities in the normallycontinuous cascading mass of tumbling material. For the cylindrical drumof this embodiment, pelletizing clay with water and steam, the criticalspeed is determined by the formula:

where RS is the critical rotational speed and D is the diameter of thedrum in feet. With a drum diameter of 10 feet, the critical speed isdetermined to be 24.2 r.p.m. In this embodiment of the presentinvention, a rotational speed of 6 r.p.m. was successfully utilized,which is well below the calculated critical speed. The production rateof the agglomerating apparatus could thus be increased considerably byincreasing the drum speed from 6 r.p.m. to any speed below 24.2 r.p.m.

The drum can be heated near the outlet end in order to dry thecompletely formed pellets. The preferred maximum moisture level of thematerial in the drum is from 10-l8% and this moisture level can be ofany of the wetting liquids given above or any combination of them.

A coating such as epoxy resin or epoxy paint may be applied to the partsof the apparatus which come into contact with the material beingpelleted in order to eliminate the possibility of contamination of thematerial.

Pellets of predispersed clay may be produced in the present invention byincluding a sutficient amount of a commercially known clay dispersantsuch as one of the polyphosphates or polysilicates, in the dry clay, ina prewetting tank, in the main spray 8, in the drum or in anycombination of these locations. A more uniform distribution of thedispersant is obtained by mixing it in the wetting liquid added inprewetting tank 3 and in the spray from nozzle 8.

The Wetting liquid may be divided into two streams and sprayed from twodifferent spray nozzles at different locations in the drum. If thesprays are placed in tandem, an even greater reduction in dusting isachieved in the drum since the downstream spray Wets down the dust notwetted down by the upstream spray.

A second spray may be used entirely for spraying a dispersant, binder,or any other additive onto the material with the first spray onlywetting the material. The dispersant or binder additive spray may beupstream or downstream from the. wetting spray in the pelletizing drum.

In lieu of or addition to adding a wetting spray, a seeded bed may beutilized in pelletizing the material. Part of the pellets formed may bebroken down and recirculated to the upstream end of the drum to seed theincoming material.

In FIG. 10, an alternative drum configuration is shown which utilizes anintegral classification system built into the drum 66. In the dischargeend 41 of the drum 66, part of the drum shell has been replaced by bandsof screen material 56 and 57, passing entirely around the circumferenceof the drum. Screen section 56 contains a tightmesh screen (such as, forexample a 40 mesh screen) for allowing only fines or very small pelletsto drop out of the drum and be collected in funnel 58. The screen 57 isa large mesh screen (such as, for example, a mesh screen) which allowsthe desirable pellets to drop out into funnel 59. Pellets and lumpswhich will not pass through either screen are discharged through outlet60 into funnel spout 61. The large lumps collected in funnel 61 arepassed to a crusher 62 which breaks the large pellets and lumps intosmall seeds and dumps them into conveyor means 63 which carries theseseeds and the fines from funnel 58 into the drum and out discharge spout64 located near the incoming stream of finely divided material enteringthrough conventional conveyor 65. The finely crushed lumps and smallpellets serve as seeds or nuclei for the incoming material and aid inthe initiation of agglomeration of the material.

In using wet pelleting by adding a liquid, a typical moisture content ina material such as clay to obtain any pelletizing in the rotating drumappears to be on the order of 12%.

If heat is applied to the drum 1 in order to dry the pellets, theminimum amount of wetness in the final dried pellet should be above 1%with a preferable wetness level of 3% to 5% for maximum dispersibilityof the material into other compounds such as paper or rubber. Thetemperature of the pellets leaving the heated drum should be around65100 C. and the pellets should exhibit a spherically shaped form with asemipolished surface.

A pellet formed in accord with the present invention when out in halfreveals a small central nucleus and shells or laminations built uponthat nucleus. These laminations are believed to be due to the wettingspray contacting the loose material in the vicinity of the pellet. Eachtime the spray hits the area near the pellet, another lamination on thepellet results.

Heat can be applied to the drum by any conventional method such asexternal gas heaters or equivalents such as electrical resistanceheaters or jets or hot gases directed at the drum.

Finished and dried pellets exit the drum at outlet 14 and pass into apellet conveying system 6 whereby they are transferred to storagevessels.

While manufacturers usually require the pelleted material to besubstantially dry, some materials will flow freely when pelletized bythis process even though they may contain up to 18% moisture.

Since a clay pellet with less than 3% mosture is ditficult to dispersefor many applications such as paper, etc., the clay pellets must containbetween 3 to 5% moisture to be acceptable to many purchasers. Yet it wasfound that by pelletizing clay using the present invention, there is notany discernible reason for drying the pellets. In fact, it isadvantageous not to do so. Pellets containing as high as 18% moisturemanufactured by the process of this invention were extremely freeflowing and do not adhere to one another when stored nor break whenhandled normally. In addition, these free flowing moist pellets areeasily dispersed in other products or into an aqueous slurry due totheir relatively high moisture content.

It has been found that the preferred pellet size distribution formaximum packing efiiciency and minimum loss to fines through attritionis as follows:

The interpretation of this distribution is, that from 25 to 55% of thepellets will not pass through a No. 5 mesh screen (largest openings), 30to 55% of the pellets will pass through a 5 mesh screen but not througha 10 mesh screen (slightly smaller openings), 5 to 25% will pass throughthe 5 and 10 mesh screens but not through a 20 mesh screen, .5 to 5%will pass through the 5, l0, and 20 mesh screens but not through a 40mesh screen, and less than 2% will pass through all the screensincluding the 40 mesh. The fraction passing through all the screens,considered as fines, may be considered undesirable because of thedifficulty in handling the particles, although the fines still consistprimarily of small pellets, with very little dusty unpelleted material.

In pelleting powdered or finely divided materials such as clay orpigments, the above pellet size distribution range will provide a pelletdistribution that has high volumetric density with free flowingproperties.

This gradation of pellets exhibits a lack of any tendency to bridge andis extremely free flowing and free of dust. Although they are notunacceptable, pellets above 5 mesh in size and below 40 mesh in sizeshould be avoided in order to obtain the highest packing density andless attrition. The optimum range of pellet sizes is between 5 mesh and40 mesh and it is often desirable to have over 50% of the pellets inthis range.

While the prior art devices, such as pin mixers or rotating tilted pans,can pelletize within this range, the pellets produced are oftenundesirable because of their low density, low compaction and theiruniformity in size. Both of these characteristics give the pellets alower bulk or pour density than those of the present invention.

Another desirable feature of the present invention involves theball-mill type of action the larger pellets exert upon the small pelletswhen the pelleted material is being dispersed into slurry or anotherproduct. This ball-mill action acids in breaking down the small pelletsand therefore eases dispersion of the material into the final products.

In four difierent pelletizing runs, the above described methods andapparatus provided uniform semi-polished pellets of good dispersibilityand attrition resistance and well within the preferred range of pelletsize distribution. The table below gives the results of the pelletizingruns.

TAB LE I Run 1 Run 2 Run 3 Run 4 Run 5 Mesh size (percent):

+5 34. 8 30. 6 42. 1 47. 0 39. 1 50. 3 46. 4 43. 2 41. 1 44. 1 13. 2 19.9 12. 8 9. 4 15. O 1. 1 2. 1 1. 3 1. 8 1. 3 40 0. 6 1. 0 0. 6 0. 7 0. 5Bulk density (#lftfi)--- 61. 1 65.4 64. 2 64. 3 63. 1 Material rate(#Imin.) 250 250 250 250 260 Percent moisture--- 10. 4 12. 6 12. 6 13. 013. 2 1 mm tti ii 'ti i (i ype we ng qm l 1 Type materla Clay Clay ClayClay Clay Drum diameter (it 10 1O 10 10 10 Drum length (it)..- 12 12 1212 1 Steam and water.

The variables involved include the bulk density, the pellet sizedistribution, maximum and minimum size of the pellets, pellet hardness,and moisture level in the finished pellet. The bulk density and pelletsize distribution are directly related to the material through-put rate,drum size and speed of rotation, the type of material pelleted, theamount of wetting liquid added in the drum, the type of wetting liquidused, the tilt of the rotating drum, if any, the bed depth of materialin the drum, and the position of the spray in the drum. The maximum andminimum size of the pellets depend mainly on the type of material to bepelleted, the type of wetting liquid used, and the retention time in thedrum. Pellet hardness is dependent upon the type of material pelletedand the type of wetting liquid used. Pellet hardness is also dependentupon bed depth since the deeper the bed of material, the greater thepressure upon the pellets in the bottom of the bed and the greatercompaction attained. Pellet wetness depends upon the amount of wettingliquid added in the drum and the amount of heat applied to thedownstream end of the drum.

It has been found in general that, within limits, an increase in themoisture added has the effect of increasing the proportion of large sizepellets produced and thus in creasing the bulk density of the point ofdiminishing returns based on sizing and breakage factors.

An increase in the speed of revolution of the pelletizing drum has, ingeneral, the efiect of increasing the number of small size pellets andtends somewhat to decrease the bulk density.

To control bed depth and retention time in the drum, the drum can betilted from inlet end to outlet end by raising one end or the other. Byraising the inlet end of the drum with respect to the outlet end,retention time will be shortened. Raising the outlet end higher than theinlet end lengthens the retention time.

Bed depth can be controlled closely by enlarging or closing off theopenings in the bafiles within the drum. In FIGS 11 and 12, the baflieswhich divide the drum into three compartments are visible. In FIG. 11,bafile 3 is shown having openings 53 placed equi-distant around thebafiie. These openings as well as the central opening 54 allow thematerial being pelletized to pass from the pelletizing compartment 39into the polishing compartment 40. Increasing the size or number of anyor all of these openings lowers the effective bed depth by allowing thematerial to pass down the length of the drum quicker. Bed depth is alsochanged by moving the openings radially inward or outward on the bafile,with bed depth decreasing as the openings are moved radially outward onthe bafile, towards the drum shell.

In FIG. 12, bafile 7 is visible, which is the bafile dividing thepolishing compartment from the discharge compartment. Bed depth in thepolishing compartment depends upon both the baflies, 3 and 7. If theopenings in baflie 3 are increased to lower bed depth in the pelletingcompartment, the opening 55 in baflie 7 must likewise be enlarged tomaintain a lower bed depth in the polishing compartment.

In the discharge compartment are lifters 42 which pick up the finishedpellets as the drum rotates and funnels them out through the outlet. Ifthe bed depth is to be lowered by enlarging the openings in bafiles 3and 7 then the size or number of lifters 42 must also be increased.

The through-put rate in the drum can also be varied by tilting the drum,enlarging the battle openings, and increasing the number of lifters. Aconstant bed depth can be maintained while the through-put rate isvaried just as in the above alteration, bed depth can be changed whilemaintaining a constant through-put rate.

Retention time is a function of drum length and diameter, tilt of thedrum, if any, and bed depth in the drum. Bed depth also depends upon therate of material input into the drum.

The advantages enjoyed by the present invention over the prior artdevices include the greater bulk densities attainable, a more freelyflowing pelleted product, an almost total absence of fines and dustresulting in less loss and less contamination, and a pelleted productwhich is easily dispersed in other compounds.

The material passing through the apparatus is completely pelletized andsubstantially all dust is removed from the material. While there arestill fines in the pelleted material, these are small pellets ratherthan dust and are not objectionable. No sizing of the pellets isrequired since the finished pellets of this invention fall within thedesired range for optimum packing density and ease of dispersion. Thepresent invention eliminates the need for classifying the pellets andeliminates the need for dust removal apparatus.

When loaded in railroad hopper cars, a clay pelleted by the process ofthis invention flowed out through the discharge spouts at the bottom ofthe hopper cars at the rate of 1 ton per minute, without the aid ofvibrators, air pads, or hammers. There was a total absence of dustduring the unloading. A non-pelletized clay was unloaded at a rate of /6of the above using vibrators and air pads.

When loaded in boxcars, material such as clay must be unloaded by frontend loaders which are basically small tractors with raisable scoops onthe front. Unloading a clay pelleted by this invention was quick andconvenient while unloading a nonpelleted clay was slow and dirty due tothe heavy dusting occurring.

In addition, the boxcar containing the pelleted clay contained more thantwice as much clay per unit volume than did the boxcar of unpelletedclay, meaning lower shipping costs for the pelleted clay.

Although a specific preferred embodiment of the present invention hasbeen described in the detailed description above, the description is notintended to limit the invention to the particular forms or embodimentsdisclosed herein, since they are to be recognized as illustrative ratherthan restrictive and it will be obvious to those skilled inthe art thatthe invention is not so limited. For example, the drum employed in thepractice of the present invention can be level or tilted. The drum maybe of any convenient length and diameter. Water can be used as a wettingliquid as can steam or both; various binder additives such as molassescan be added to the water, and other wetting liquids such as oils ororganic liquids can be substituted for water. The drum can also be usedfor dry pelletization using the seeded bed principle whereby a portionof the finished pellets are crumbled and refed back into unpelletizedmaterial to provide seeds or nuclei for newly forming pellets. The innersurface of the drum may be smooth, rough, or may have fins or liftersattached to it to agitate the bed of material. Also, more than one spraycan be utilized in the drum and a commercially available dispersant canbe added to the material or to the wetting liquid or to a separate sprayto provide a predispersed product, such as predispersed kaolin clay.Additional clay of the same or other types may be added in slurry formto that being pelletized by the spray. The drum can be heated near itsoutlet end by gas or electric heaters or can be used without heating. Aswill be noted the present invention substantially reduces the dustingproblem. In the absence of the present invention it is not uncommon tolose 3 to 6% of the material shipped to the atmosphere. This inventionhas particular advantages for export shipments where density is of thegreatest importance and multiple handling is required. The invention isdeclared to cover all changes and modifications of the specific exampleof the invention herein disclosed for purposes of illustration, which donot constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A method for agglomerating finely divided clay into pellets having anoptimum density and a size range which exhibits maximum effectivepacking density and attrition resistance comprising:

(a) introducing finely divided clay having a moisture content of about1.5 to 5% by weight into one end of a rotating cylindrical drum andtumbling said material therein;

11 12 (b) contacting said tumbling clay with a liquid wetting (e)discharging said formed pellets from said drum.

agent in said drum wherein said clay begins to curl 2. The method ofclaim 1 wherein said clay prior to back and tumble down the side of saidrotating drum; Step (a) is heated to a temperature of about 75 to 95 C.(c) spraying said liquid wetting agent at said curl in and thetemperature of the liquid wetting agent sprayed the form of a hat widespray having a spray angle 5 onto said tumbled clay is about 75 to 100C.

attitude, as shown at (4.8) in FIG. 3 of the drawings,

in the range of 38 to 85 and a spray angle and an References Cited angleof inclination, as shown at (21?) and 24) of UNITED STATES PATENTS $5.respectwely drawmgs 3,555,133 1/1971 Gentaz 254 11 (d) continuingrotation of said drum at a speed below 368764o 8/1972 at a] 264 117 thecritical speed RS defined by 3,277,218 10/ 1966 Dollmger 264-4173,597,170 8/1971 Dollinger 264-417 Zi-fi OTHER REFERENCES 7Aggiomeration, Chemical Engineering, mag., Dec. 4,

wherein D is the diameter of the drum in feet, to form 1967 McGraw-HluNew York pellets having a size range exhibiting maximum ef- ROBERT WHITEEX fective packing density of from about to nmafy ammer pounds Per cubicf t and I. R. HALL, Assistant Examiner

